The invention relates to a wheel assembly for a motor vehicle and, in particular, a wheel assembly that is configured for suspending the wheel of a motor vehicle on one side and that includes a brake disc which is part of a disc brake and which is fixed, when viewed in the radial direction, to a wheel disc on the outer circumference of the wheel assembly in close vicinity to a wheel rim.
A construction of a conventional wheel and its bearing consists of the following components: a wheel bearing, a wheel hub having a wheel mounting flange and a wheel rim with a tire. The wheel rim is fastened to the wheel mounting flange by use of wheel screws in such a way that the brake disc is clamped between the rim and the wheel mounting flange. Such a wheel bearing arrangement is described in DE 101 32 429 A1. In this case, the maximum friction radius of the brake disc is determined by the following chain of measurements: the inner radius of the wheel rim minus the height of the brake caliper bridge minus half the lining height. Therefore, in the case of high powered vehicles it is often necessary to use a larger rim in order to accommodate the required size of the brake disc.
When dimensioning the brake disc, a goal should be to make the friction radius as large as possible, because it reduces the clamping force of the brake caliper and, thus, its weight. The brake caliper bridge can be dimensioned smaller; and the hydraulic piston can be correspondingly smaller. However, with an increasing diameter of the brake disc, the weight of the brake disc also increases.
However, it is also possible to achieve a large friction radius if the brake caliper surrounds or grips the brake disc from a radially inner side. That is, the height of the brake caliper bridge is excluded from the chain of measurements. This necessitates that the brake disc be fastened to the rim or that the wheel mounting flange, or more specifically the wheel disc, has to be designed approximately as large as the inside diameter of the rim of the wheel and that the internally surrounded brake disc be fastened thereto.
Such a design is described in EP 018 37 48 A1 as a wheel assembly having a disc brake that is configured for vehicles and includes a disc carrier, which has the shape of a cup and has a base member secured to a wheel hub, as well as a drum member, which extends axially inwards at a small radial spacing from a wheel rim and is securely connected to the radially outer edge of a brake disc. Furthermore, a stationary housing of the wheel bearing supports a brake caliper, which is supported at the radially inner edge of the brake disc, supports the brake pads, which are arranged on both sides of the brake disc and has an actuating device on at least one side of the brake disc. Ventilating channels are present radially inside the wheel rim.
To date, an internally surrounded brake disc that is fixed to the rim was known only on motorcycles. The background is that in this case, as compared to an automobile, no significant lateral forces are generated. The wheel bearings sit directly in the wheel, so that the brake disc receptacle can be manufactured with close tolerance to the bearing seats. In contrast, in the case of single sided wheel suspensions the production tolerances and the deformation of the rim under lateral force are the factors contributing to the elimination of a lateral run-out of a brake disc that is fixed to the rim. The brake pads are pushed back, so that when the brake is applied, the result is an unacceptable dead stroke until the brake pads engage again. In addition, rotational vibrations of the steering wheel are generated. The lateral run-out is controlled by manufacturing the wheel hub flange and the brake disc very precisely. Only the deformation between the wheel carrier and the wheel hub flange has an effect on the lateral run-out. If an internally surrounded brake disc were to be fastened to a conventional rim of such a single sided wheel suspension, then the distortion of the rim alone would exceed the permissible tolerances due to the uneven tightening of the wheel screws.
Changing the wheel with a brake disc that is fixed to the rim is much more difficult, because the disc has to be extracted from the brake caliper during the disassembly and then reinserted into the brake caliper during the assembly. The risk of a human error occurring during assembly or, for example, the risk of applying the brake when the brake disc is extracted is high.
In order to achieve the necessary lateral run-out in the assembled state for a wheel assembly according to the state of the art, the wheel hub flange on the outer side of the wheel is overtightened together with the wheel bearing on the inner side of the wheel. In this case then the brake disc tolerances accumulate with those of the rim and the tolerances caused by handling, for example, due to uneven tightening of the wheel screws.
The object of the present invention is to provide a wheel assembly that is configured for a motor vehicle and that is as light as possible. Therefore, such a wheel assembly is designed to meet the requirements while at the same time avoiding as many of the aforementioned drawbacks as possible.
The invention achieves this and other objects by providing a wheel assembly that is configured for suspending the wheel of a motor vehicle on one side and that includes a brake disc, which is part of a disc brake and which is fixed, when viewed in the radial direction, to a wheel disc on the outer circumference of the wheel assembly in close vicinity to a wheel rim, the brake caliper of the disc brake surrounding the brake disc over an inner circumference of the brake disc and being fixed to a wheel carrier that supports a stationary ring of a wheel bearing, which has a rotating ring that supports a wheel hub that is connected to the wheel disc in a rotationally and axially fixed manner. The wheel assembly is characterized in that the connection of the wheel disc to the wheel hub is formed by a press fit or by a spur toothing, in particular a Voith Hirth coupling.
In addition, a non-driven wheel can be designed specifically for lateral force, because no driving or braking torques are introduced by way of the wheel disc, a feature that also offers advantages with respect to weight.
Advantageous embodiments of the invention provide that the wheel hub is connected to a drive shaft on the side of the wheel bearing that lies inside the wheel by way of an additional spur toothing, in particular, an additional Voith Hirth coupling. Then, the axial prestress of the spur toothing, the additional spur toothing and/or the press fit can be achieved in an advantageous way by use of a screw connection that is accessible on the side of the wheel hub that lies outside the wheel. This arrangement allows the wheel disc to be easily removed by loosening the screw connection. Such a feature significantly simplifies the maintenance work, for example, on the brake.
Preferred embodiments of the invention provide that the brake disc is fastened to the wheel disc in a floating manner or in an elastically flexible manner in the radial direction. This feature can be achieved, for example, by use of a retaining ring, which is elastically flexible in the radial direction and is fixed to the wheel disc. Such a brake disc holder can be easily designed in an elastic manner owing to the low force level of the brake force applied a long way on the outside, a feature that allows the brake disc to expand without restriction in an advantageous way. As a result, a so-called cupping of the brake disc is avoided; and local axial deformations of the wheel disc under lateral force are not transmitted to the brake disc.
If the wheel is split into two functional units so that the wheel screws connect the wheel rim to the wheel disc, then a wheel hub flange that exhibits a significantly enlarged diameter and that also supports the internally surrounded brake disc remains on the vehicle when the wheel is disassembled. Then, when changing the tire, the wheel rim is unscrewed, as the tire carrier, from the wheel disc.
The brake disc can dispense with the securely connected cup and, hence, can be punched advantageously from a sheet, a feature that offers advantages with respect to weight and cost. Moreover, the smaller amount of required clamping force due to the larger friction radius reduces the weight of the brake caliper, whereas the possibility of a large installation space for the brake caliper bridge permits high rigidity in conjunction with less weight. In addition, an improved transmission ratio enables a smaller brake force booster.
In addition, it is advantageous for the wheel rim to be made of an extruded hollow chamber profile. In an especially advantageous embodiment of the invention, the wheel rim and/or the wheel disc can be made of aluminum or magnesium or of a synthetic plastic material, in particular, reinforced with carbon fibers or glass fibers. In this case, the wheel hub and the wheel disc can also be composed of different materials.
The divided construction of the wheel hub and the wheel disc permits a wide scope of design options; and in terms of the structure and materials without the restrictions that are associated with a screw connection of the wheel according to the state of the art. In this case, all of the forces and moments have to be transmitted from the wheel hub flange over the screw connection to the rim. A component connection by way of a press fit or, more specifically, a Voith Hirth coupling, exhibits advantageously a higher stiffness in conjunction with an improved non-positive connection. The rim base can be made of a bent extruded profile, so that the result is that the rim base is also stiffer compared to a conventional rim, because the largest proportion of the material may be found in close vicinity to the neutral fibers. Inexpensive twin rims, for example, for winter tires, are possible or in the case of replacement due to damage, because only the rim band has to be replaced.
The wheel unit and the brake caliper can be configured in such a way that they can be easily replaced, as compared to a wheel or a brake according to the state of the art. As a result, a solution according to the invention can be used, for example, only for high powered vehicles, whereas the less powerful variants can be equipped in parallel with a wheel and brake system according to the state of the art. This arrangement lends itself especially well to expensive wheel designs, such as, for example, wheel designs in carbon fibers. Similarly, retrofitting in the accessory business is also contemplated with this arrangement.
A particularly advantageous embodiment of the invention is characterized in that the wheel bearing is secured over its inner ring on the wheel hub on the inner side of the wheel by means of a cap nut. As an alternative, the wheel bearing can also be secured over its inner ring on the wheel hub on the inner side of the wheel by means of an enlargement of the outer diameter of the wheel hub, in particular by beading. In this case the enlargement of the outer diameter of the wheel hub for securing the wheel bearing can be achieved within the framework of manufacturing the spur toothing on the wheel hub. In particular, this can be done by way of a clamping element within a clamping process for the wheel hub and, in particular, in one working step. Therefore, a connection, which cannot be loosened at least in the case of service, is advantageous, because the receptacle for the brake disc and the receptacle for the rim base can be overtightened in the assembled state with the wheel bearing; and, thus, a maximum amount of lateral run-out is achieved. This applies especially if the brake disc holder and the wheel disc are constructed in one piece. In addition, the elimination of the conventional wheel hub flange makes it possible for the width of the wheel bearing to be larger whereas the diameter of the wheel bearing is smaller, so that the result is less bearing and sealing friction or that the depth of the wheel disc can be larger for high rigidity.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.